Al-Si-Sn Bearing Alloy and bearing composite

ABSTRACT

An aluminum base bearing alloy having outstanding seizure resistance, fatigue resistance and wear resistance is provided. The alloy comprises, in addition to aluminum, 0.5-5 wt. % Si and 1.5-35 wt. % Sn and contains at least 5 nodular Si particles having a diameter of at least 5 μm per 3.56×10 -2  (mm) 2  of cross-sectional area of the alloy. The bearing alloy may optionally contain at least one additional element selected from Pb, In, Tl, Cd, Bi, Cu, Mg, Cr and Mn. A bearing material is provided by pressure welding the aluminum base bearing alloy to a backing steel sheet.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to aluminum base bearing alloys and bearingmaterials and, paricularly, to aluminum base bearing alloys in which aspecified number of silicon particles of a specified size are dispersedin the aluminum matrix.

(2) Background of the Invention

Aluminum alloys are widely used as bearings in internal combustionengines, e.g., as connecting rod bearings and crankshaft bearings inautomobile and marine engines. These bearings are resistant to corrosionin the engine environment and thus are highly advantageous for such use.

Materials employed as bearings in internal combustion engines arerequired to withstand high loads and high temperatures. Much effort hasbeen directed in recent years, therefore, to providing aluminum basebearing alloys having high resistance to seizure, fatigue and wear underthe conditions encountered in these engines.

U.S. Pat. No. 4,153,756 discloses Al-Sn base bearing alloys having a lowdegree of softening and, consequently, high fatigue strength, under hightemperature conditions. The alloy is provided by adding chromium orzirconium to a basic alloy consisting of 10 to 30 wt.% tin and theremainder aluminum. Copper or both copper and beryllium can also beadded to the alloy.

An-Sn base bearing alloys comprising 3.5-35 wt.% of Sn, 0.1-1.0 wt.% ofCr and 1-10 wt.% in total of one or more members selected from Si, Cr,Mn, Sb, Ti, Zr, Ni and Fe, the remainder being aluminum, are alsodisclosed in the prior art as having high fatigue strength and,additionally, good wear resistance.

G. C. Pratt and C. A. Perkins in a paper entitled "Aluminum BasedCrankshaft Bearings for the High Speed Diesel Engine", SAE TechnicalPaper Series 810199 (1981), describe the development of an enginebearing lining alloy for the high speed diesel engine and which has thecomposition Si (11 wt.%), Cu (1 wt.%) and the remainder Al. The alloy isdescribed as having superior seizure resistance as compared to leadbronze on test rigs under conditions of sparse lubrication and cntrolledmisalignment. It is further described that the casting procedure adoptedand the subsequent processing of the alloy to bimetal ensure that thesilicon particles are restricted to a few microns in size and that thesilicon particle size is an important factor in determining the extentof compatibility (defined in the paper as the resistance of a bearingalloy to local welding on to a steel counterface); the highest degreebeing obtained only when there is a complete absence of coarseparticles. The casting procedure and processing of the alloy to bimetal,however, are not described.

The mere inclusion of silicon in an aluminum base bearing alloy,however, does not ensure that the bearing alloy will possessconsistently superior resistance to seizure, fatigue and wear under thesevere loads and temperature conditions encountered in modern internalcombustion engines and, particularly, in automobile engines which haveshafts made of spheroidal, or nodular, graphite cast iron or othercoarse material.

It is an object of the present invention, therefore, to provide analuminum base bearing alloy and bearing composite which consistentlypossesses a superior balance of seizure, fatigue and wear resistanceunder high loads and high temperatures and when used as a bearingsurface with nodular cast iron materials.

SUMMARY OF THE INVENTION

According to the present invention this and other objects are obtainedby providing an aluminum base bearing alloy which contains 0.5-5 wt.% Siand 1.5-35 wt.% Sn and in which at least 5 particles of Si which have anodular, or "lumpy", shape and a diameter of at least 5 μm are providedper 3.56×10⁻² (mm)² of cross-sectional area of the bearing alloy. Thebearing alloy of the invention may optionally include up to 8 wt.% ofPb, In, Tl, Cd or Bi; up to 2 wt.% of Cu or Mg and up to 1 wt.% of Cr orMn for providing other desired properties.

In other embodiment of the invention a bearing material is provided bypressure welding the bearing alloy to a backing steel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the seizure unit loads (seizure resistance) ofaluminum base bearing alloys according to the present invention as afunction of Si content of the alloy.

FIG. 2 is a graph showing the seizure unit loads versus silicon contentof alloys having the same composition as those of FIG. 1 but in whichthe Si particle size is not controlled,

FIG. 3 is a graph showing a comparison of the wear resistance versus Sicontent of aluminum base bearing alloys according to the presentinvention with that of similar alloys in which Si particle size is notcontrolled.

FIG. 4 is a graph showing the fatigue unit loads (fatigue resistance) ofaluminum base bearing alloys according to the present invention as afunction of the Si content of the alloys.

FIG. 5 is a graph showing seizure unit loads of aluminum base bearingalloys according to the present invention as a function of surfaceroughness of a supported shaft.

FIG. 6 is a graph showing seizure unit loads of a thrust bearing as afunction of the number of Si particles of 10-20 μm of aluminum basebearing alloys according to the present invention.

FIG. 7 is a graph showing seizure unit loads of an aluminum base bearingalloy according to the present invention as a function of oiltemperature.

FIG. 8 is a graph comparing seizure unit loads of an aluminum basebearing alloy according to the present invention with those of aconventional Al-Sn-Cu alloy as a function of the type of supportedshaft.

DESCRIPTION OF PREFERRED EMBODIMENTS

The aluminum base bearing alloy according to the present inventioncontains 0.5-5 wt.% of Si and 1.5-35 wt.% of Sn. The superior resistanceto seizure, fatigue and wear of the bearing alloy of the presentinvention is not obtained when the alloy contains less than about 0.5wt.% of Si. Amounts of Si of more than about 5 wt.% do not providesignificantly better properties (although these high amounts providebetter results under conditions of high-load and use of low viscosityoil) and tend to decrease the wear resistance and strength of thealloys. Preferably, the alloy contains 2-5 wt% of Si.

The silicon (Si) is present in the form of procipitates in the aluminummatrix of the alloy of the invention. At least 5 particles per 3.56×10⁻²(mm)² of cross-sectional area of the bearing alloy of the Si must be inthe form of nodular particles having a diameter of at least 5 μm. Asemployed herein to define the shape of the particles, the term "nodular"is intended to mean an irregular, rounded lump as opposed to flatflake-like or needle-like particles. Nodular particles are requiredsince flat or needle-like particles are brittle and may tend todisintegrate during use and adversely affect the antiseizing propertiesof the bearing alloy.

Also, as employed herein, the term "diameter" is intended to refer tothe maximum dimension of a particle when viewed in a cross-sectionalarea of the alloy.

At least 5 nodular Si particles having a diameter, or size, of at least5 μm must be provided in a cross-sectional area of the bearing alloy of3.56×10⁻² (mm)². This area is chosen for convenience and is based on theviewing area of the microphotography equipment of the inventors. Thenumber of Si particles per unit area can be modified by employing theappropriate conversion factors. For example, the above-describedparticle number/area limitation corresponds to 1.4×10⁸ particles per m².It is also noted that the number of particles per cross-sectional areaof the bearing alloy is that determined in a horizontal cross-section ofa sheet of the alloy, i.e., a cross-section that is parallel to thesurface of the sheet (and viewed in a direction perpendicular to thesurface thereof), when prepared according to a process as describedbelow. The size of Si particles measured in a vertical cross-section ofa sheet of the alloy is smaller than that measured in a horizontalcross-section. It is further noted that the quantity limitationsdescribed above may not be fulfilled on the surface of a sheet of thealloy directly after its machining.

If the nodular particles of silicon are less than 5 μm, the bearingalloy will not have exceptional seizure or wear resistance. On the otherhand, there is a practical upper limit of about 40 μm for the size ofthe Si particles because with bearing alloys containing particles aboveabout 40 μm machining of the bearings becomes difficult.

To achieve the desired levels of seizure resistance the number of thenodular particles above 5 μm per 3.56×10⁻² (mm)² of cross-sectional areaof the alloy must be at least 5. The maximum number of particles of anygiven size is of course limited by the amount of Si contained in thealloy. Typically, the desired properties of the aluminum base bearingalloys of the present invention are achieved when the number of Siparticles having a size of at least 5 μm and, particularly, having asize between 5-40 μm is less than the maximum number of particlespossible based on the amount of Si contained in the alloy; the balanceof the Si being particles of less than 5 μm.

Seizure resistance of the bearing alloy according to the presentinvention increases as the size of the nodular Si particles increases.On the other hand, the number of larger particles is limited because thelarger particles tend to decrease the fatigue resistance of the bearingalloys. To obtain bearing alloys having the highest seizure resistancethe bearing alloy of the invention will preferably contain, per3.56×10⁻² (mm)² per cross-section area, at least 5 particles having adiameter of 5 μm or higher and at least 5 particles greater than 10 μmin diameter. More preferably, the alloy will contain, per said unitarea, at least 5 particles having a size of 5 μm or higher, at least 5particles having a size greater than 10 μm and at least 1 particlegreater than 20 μm (and less than about 40 μm for the reasons notedabove). However, for bearing alloys according to the present inventionhaving the highest level of seizure resistance, the fatigue resistanceis somewhat lower as may be seen by referring to the data of the tablespresented below.

The improved seizure reistance of the bearing alloy according to thepresent invention in which the shape, size and number of Si particlesare controlled according to the limitations described above is believedto be due to the ability of the Si particles to prevent the well-knownadhesion phenomenon between aluminum base bearings and the shaftssupported thereby and to reduce the surface roughness of the shafts.Aluminum tends to rub off onto a rotating shaft and to adhere theretoand there is a tendency for the aluminum on the shaft to adhere to thatof the bearing. It is believed that the nodular Si particles tend toremove the aluminum from the shaft.

The apparent ability of the silicon particles of the aluminum basebearing according to the present invention to reduce the surfaceroughness of the shaft to be supported by the bearing is most pronouncedwith the use of shafts having a hard and coarse surface and,particularly, with the use of nodular graphite cast iron shafts. Withconventional aluminum base bearings, grinding burrs which are formedaround the graphite particles on the surface of the shaft tend to grind,or wear, the surface of the bearing material. The nodular Si particlesof the alloy according to the present invention, however, are believedto smooth over the roughness of the surface of the nodular shaftsbecause of the number and size of the hard Si particles. It is notedthat the improved wear resistance and antiseizing property of thebearing alloy according to the present invention is not obtained unlessthe shape, size and number of the Si particles are controlled as notedabove.

The seizure resistance, fatigue resistance and wear resistance of thebearing alloy according to the present invention are determinedaccording to tests under dynamic loads which are described more fullybelow in conjunction with specific embodiments of the alloy. Theseproperties cannot be defined easily in quantitative terms because thevalues depend on the design of the testing equipment and test conditionsand such equipment and conditions are not standard in the art.

The aluminum base bearing alloy according to the present invention alsocontains tin in an amount of 1.5-35 wt.%. The tin is added mainly forthe purpose of lubrication. An amount of tin of greater than 35%,although improving comformability and low friction properties, reducesthe hardness and strength of the bearing alloy. On the other hand, ifthe amount of tin is less than 1.5%, the bearing alloy is too hard anddoes not have sufficient conformability. The addition quantity of thetin within the range of 1.5-35 wt.% can be determined according to theexpected use of the bearing alloy. Generally, the amount of tin is lowif the bearing is to be employed under large loads. For use under lightloads, the amount of tin can be higher. The seizure resistance of thebearing alloy of the present invention is also increased as the amountof tin is increased.

In other embodiments of the aluminum base bearing alloy according to thepresent invention, the alloy, in addition to containing the silicon andtin, may also contain at least on element from at least one of thefollowing groups of elements: (a) lead (Pb), indium (In), thallium (Tl),cadmium (Cd) and bismuth (Bi); (b) copper (Cu) and magnesium (Mg); and(c) chromium (Cr) and manganese (Mn). The elements Pb, In, Tl, Cd and Bican be used alone or in any combination and are employed in a totalamount of from about 0.5-8 wt.%. Cu and Mg are employed alone or in amixture thereof and are employed in an amount of from about 0.1-2 wt.%.Cr and Mn are employed alone or in a mixture thereof and are employed inan amount of from 0.1-1 wt.%.

The addition of 0.5-8 wt.% of Pb, In, Tl, Cd and/or Bi to the bearingalloy improves the conformability and seizure resistance of the bearingmaterial. An amount of less than 0.5 wt.% does not appreciably affectthe properties of the alloys. Amounts greater than 8 wt.% are notdesirable since they tend to decrease the melting point of the Sn.Additionally, the total addition quantity of these elements togetherwith the addition quantity of the tin should not be more than about 35wt.% since the fatigue resistance of the bearing alloy decreases as thecombined amounts of these elements increases.

Cu and/or Mg can be contained in the bearing alloy of the invention inan amount of 0.1-2 wt.%. The Cu and/or Mg have an important effect onthe hardness of the aluminum matrix and reduce the lowering of thehardness at high temperatures. The hardness of the alloy is increased asthe amount of Cu and/or Mg is increased within this range whereas theseizure resistance decreases. Therefore, the amount of Cu and/or Mgemployed is chosen so as to obtain a desired balance between thehardness and seizure resistance of the bearing alloy. An increase in thehardness of the alloy is not obtained with amounts of Cu and/or Mg ofless than 0.1 wt.%. Amounts of these metals of more than 2.0 wt.% reducethe rolling property of the bearing alloy and lower theanti-corrosiveness. Furthermore, the Mg exists as a solid solution inthe aluminum matrix and is liable to deposit during the annealing if theamount thereof is more than 2.0 wt.%.

The addition of 0.1-1 wt.% of Cr and/or Mn to a bearing alloy accordingto the present invention is also effective in preventing the lowering ofthe hardness of the alloy at high temperatures (although to a lesserextent than the addition of Cu and/or Mg) and in preventing thecoarsening of Sn particles. When the quantity of the Cr and/or Mn isless than 0.1 wt.%, the improvement in high temperature hardness cannotbe expected. The effect of the addition of amounts of more than 1.0 wt.%is not appreciable. The Cr and/or Mn form fine precipitates in thealuminum matrix. The Cr and/or Mn also serve to enhance the effects ofthe addition of the Cu and/or Mg and of the Pb, In, Tl, Cd and/or Bi.

The aluminum matrix of the bearing alloy according to the presentinvention preferably has a Vickers hardness (Hv) of from about 30 to 60.If the aluminum matrix is too soft, the load capacity of the bearing isinsufficient and when a load is applied to the bearing, the siliconparticles are pushed into the surface. If the aluminum matrix is toohard, when a shaft contacts the bearing surface, the silicon particlesmay be removed from the surface and will not become embedded again butwill roll between the shaft and the bearing and cause excessive wear.

The aluminum base bearing alloy according to the present invention isprepared by melting aluminum in a gas furnace and adding desired amountsof Si and Sn and, depending on the desired properties of the alloy, theoptional elements such as Pb, In, Cu, Cr and the like, to the moltenaluminum according to the conventional techniques. The molten alloy iscast and the cast alloy is then subjected to steps of peeling; repeated(if necessary) rolling and annealing to obtain a sheet of the alloy ofdesired thickness; slitting; annealing; sanding; brushing and the liketo obtain bearing alloy pieces. These pieces are then applied to backingsteel sheets by conventional pressure welding techniques to obtainbimetal pieces which are then subjected to annealing and coiling. Theseannealed pieces can then be worked into plain bearings. The foregoingsteps employed in the process of the present invention are, per se,known in the art relating to the preparation of aluminum base bearingsand are dislcosed, for example, in U.S. Pat. Nos. 3,078,563; 3,093,885;3,104,135; 3,167,404; 3,300,836; 3,300,838 and 3,384,950. The processesfor preparing aluminum based bearings disclosed in these patents areincorporated herein by reference.

Control of the size and number of nodular silicon particles in thebearing alloy which meet the limitations described above, i.e., at least5 particles having a size of at least 5 μm, may be obtained bycontrolled annealing of the cast alloy according to conditions notpreviously disclosed in the art. Specifically, in the process employedin the present invention, during the rolling and annealing of the castalloy, annealing is carried out at a temperature of 280°-550° C. for 1.5to 6 hours. Following slitting, annealing is carried out at atemperature of greater than 350° C. and up to 550° C. for 1.5 to 6 hoursfollowed by controlled cooling at a rate of less than 200° C. per hour.Following bonding to the backing steel by pressure welding, annealing iscarried out at a temperature of 300°-400° C. for 1 to 2 hours.

The distinctions between the process employed in the present inventionfor obtaining the aluminum base bearing alloy and bearing compositewherein the alloy contains silicon particles of specified shape, sizeand number and the prior art processes may be better understood byreferring to Table 1.

As noted previously, the aluminum base bearing composite according tothe present invention is prepared by pressure welding the aluminum basebearing alloy according to the present invention to a backing steelaccording to conventional techniques and annealing the resultantcomposite at a temperature of 300° to 400° C. for 1 to 2 hours. Thealuminum base bearing composite according to the present invention canbe used as a bearing for internal combustion engines under conditions ofhigh load without the need of a lead overlayer, or overplate, which isrequired for conventional aluminum base bearings.

                                      TABLE 1                                     __________________________________________________________________________                                    Process Employed in                           Step         Prior Art Process(es)                                                                            Present Invention                             __________________________________________________________________________     (1)                                                                             Dissolution                                                                             Melting at 670-750° C.                                                                     ←                                        (2)                                                                             Casting   1.5-2.5 m/min       ←                                                    (1-2 m/min)                                                       (3)                                                                             Peeling   Recuce thickness about 2 mm                                                                       ←                                        (4)                                                                             Rolling   2-6 mm/pass         ←                                        (5)                                                                             Annealing 180-230° C. for about 1.5 hours                                                           280-550° C. for                                     (≦350° C. for about 1.5 hours)                                                     1.5 to 6 hours                                             Steps (4) and (5) repeated, if necessary                          (6)                                                                             Rolling   2-6 mm/pass         ←                                        (7)                                                                             Slitting  No conditions specified                                                                           ←                                        (8)                                                                             Annealing 180-230° C. for about 1.5 hours                                                           Greater than 350° C.-550°                                       C.                                                         No control of cooling speed                                                                      for 1.5 to 6 hours                                         (≦350° C. for about 1.5 hours                                                      Cooling speed: less than                                   No control of cooling speed)                                                                     200° C. hour                            (9)                                                                             Sanding   0.01-0.05 mm        ←                                        (10)                                                                            Brushing  No conditions specified                                                                           ←                                         (11)                                                                           Pre-heating                                                                             100-180° C.  ←                                                    (60-140° C.)                                                                               ←                                       (12)                                                                             Sanding   0.005-0.05 mm       ←                                       (13)                                                                             Cleaning  Trichloroethylene   ←                                       (14)                                                                             Ni-plating                                                                              Thickness < 5μm  ←                                       (15)                                                                             Pre-heating                                                                             8C-230° C.   ←                                       (16)                                                                             Bonding   Reduction ratio: 45-55%                                                                           ←                                          (Pressure welding)                                                                      (45-60%)                                                         (17)                                                                             Annealing 180-230° C. for about 1.5 hours                                                           300-400° C. for 1-2 hours                           (≦350° C. for about 1.5 hours)                     (18)                                                                             Coiling   No conditions specified                                                                           ←                                       __________________________________________________________________________     Note:                                                                         Conditions in parentheses are isolated teachings in the prior                 Steps (12)-(15) apply to the backing steel to which the alloy is bonded i     step 16.                                                                 

The present invention may be better understood by referring to theaccompanying drawings in light of the following description and data.

The seizure resistance, fatigue resistance and wear resistance datapresented below and shown in the drawings were measured under conditionsas described in Table 2. The seizure resistance tests measure the staticload necessary to cause seizure at constant oil temperature. The fatigueresistance test measures fatigue limits under dynamic load conditionsand under forced lubrication with lubricant oil of a constanttemperature and by using a quenched shaft material rotating at 3000 rpmand with 10⁷ times repetition of stressing. The wear resistance testmeasures the amount of wear of a bearing material at a constant loadwith respect to a shaft rotating at a constant speed over a definiteperiod of time.

Aluminum base bearing alloys according to the present invention wereprepared by a process as described above employing the conditions listedin Table 1. Each of the alloys contained, in addition to aluminum, 15wt.% Sn, 3 wt.% Pb, 0.5 wt.% CU, 0.4 wt.% Cr and an amount of Si aslisted in Table A below. Each of the samples of Table A was annealed ata temperature of 350° C. for 1.5 hours in step (5) of the process (referto Table 1). Cooling conditions following annealing were not controlled.Annealing and cooling conditions in step (8) of the process werecontrolled as listed in Table A so that each of the alloys, with theexception of sample 1 having an Si content of 0.1 wt.%, containedapproximately 30 nodular particles of Si having a size of 5-10 μm,approximately 11 nodular particles of Si having a size of more than 10and up to 20 μm, and approximately 3 nodular particles of Si having asize of more than 20 and up to 40 μm, the balance of the Si beingparticles of less than 5 μm. Sample 1 did not contain any particles ofSi of greater than 10 μm because of the low Si content.

                  TABLE 2                                                         ______________________________________                                        Tester       Test Conditions                                                  ______________________________________                                        A - Seizure Tester                                                                         Shaft material: Nodular                                                       Lubricant type: SAE 10W-30                                                    Shaft surface roughness: 0.4-0.6 μm Rz                                     Oil temperature: 140 ± 2° C.                                        Rotation speed: 1000 rpm                                                      Shaft diameter: 52 mm                                                         Shaft hardness: Hv 200-300                                                    Urging load: 50 kg/cm.sup.2 /30 min                                           (increase gradually)                                                          Bearing surface roughness: 1-1.8 μm Rz                                     Bearing inner diameter: 52 mm                                    B - Fatigue Tester                                                                         Shaft material: AISI 1055 (forged)                                            Lubricant type: SAE 10W-30                                                    Shaft surface roughness: 0.8 μm Rz                                         Oil temperature: 140 ± 2.5° C.                                      Oil pressure: 5 kg/cm.sup.2                                                   Rotation speed: 3000 rpm                                                      Shaft diameter: 52 mm                                                         Shaft hardness: Hv 500-600                                                    Stress repititions: 10.sup.7 times                                            Bearing surface roughness: 1-1.8 μm Rz                                     Bearing inner diameter and width:                                             52 × 20 mm                                                 C - Wear Tester                                                                            Shaft material: Nodular                                                       Lubricant type: Liquid paraffin                                               Shaft surface roughness: 0.8-0.9 μm Rz                                     Rotation speed: 100 rpm                                                       Shaft diameter: 40 mm                                                         Shaft hardness: Hv 200- 300                                                   Urging load: 35 kg                                                            Term of test: 5 hours                                            D - Seizure Tester                                                                         Rotary disc material: Nodular                                                 Disc surface roughness: 1-1.2 μm Rz                                        Lubricant type: SAE 10W-30 (1)                                                Kerosene (10)                                                                 Sliding speed: 15 m/sec                                                       Lubricant condition: Pad oiling system                                        Urging load: 10 kg/10 min                                                     (increase gradually)                                                          Bearing surface roughness: 1-1.8 μm Rz                        ______________________________________                                    

The seizure resistance of these alloys were measured employing theconditions for seizure tester A listed in Table 2. Each sample wastested three times under the same conditions. The seizure unit loadvalues obtained are shown in FIG. 1.

For comparison, alloys of the same composition as those of Table A wereprepared according to the same process but without control of the sizeand number of the Si particles by carrying out annealing in step (8) at300° C. for 1.5 hours and by not controlling the cooling rate of theannealed samples. Seizure resistance of these alloys determined in thesame manner as those of the alloys of Table A are shown in FIG. 2.

It may be seen by referring to the data of FIGS. 1 and 2 that thealuminum base bearing alloys of the present invention in which theshape, size and number of silicon particles are controlled, have farbetter seizure resistance than similar alloys prepared according toprior art procedures where there is no control of silicon particleformation.

                  TABLE A                                                         ______________________________________                                                    Annealing Condition (Step (8)- Table 1)                                             Temperature,       Cooling                                  Sample No.                                                                            Si (wt. %)                                                                              (°C.)                                                                             Time (Hr)                                                                             (°C./Hr)                          ______________________________________                                        1       0.1       520        5.5     80                                       2       0.5       500        5.0     100                                      3       1         475        4.5     120                                      4       3         450        4.0     140                                      5       5         425        3.5     160                                      6       7         400        3.0     180                                      7       11        360        1.5     200                                      ______________________________________                                    

The wear resistance of the alloys of Table A was measured according tothe conditions listed for wear tester C in Table 2. The wear data forthese alloys are shown in FIG. 3 (labelled "Control"). The wearresistance of alloys of the same composition but produced withoutcontrol of the Si particles was similarly determined and the data arealso shown in FIG. 3 (labelled "No control").

The aluminum base bearing alloys according to the present invention areseen to be markedly superior in wear resistance.

The fatigue resistance of the alloys of Table A was measured accordingto the conditions for fatigue tester B listed in Table 2. The fatigueunit load data is shown in FIG. 4. It is seen that the fatigueresistance of the alloys of the invention remains relatively constant asthe Si content is varied within the range of 0.5-5.0 wt.%.

Aluminum base bearing alloys according to the present invention havingthe composition: Si 3 wt.%, Sn 15 wt.%, Pb 3 wt.%, Cu 0.5 wt.%, Cr 0.4wt.%, the balance being aluminum, were prepared according to the processdescribed above and employing the conditions for the process employed inthe present invention described in Table 1. Annealing conditions in step(8), Table 1, were varied to produce alloy samples A-1 to A-3, B-1 toB-3, C-1 to C-5, D-1 to D-3, E-1 and E-2 containing the distribution ofnodular Si particles set forth in Table B.

                                      TABLE B                                     __________________________________________________________________________    Sample                                                                            No. of Si particles/3.56 × 10.sup.-2 (mm).sup.2                     No. less than 5 μm                                                                     5-10 μm                                                                         10 < -20 μm                                                                        20 < -30 μm                                                                        30 < -40 μm                               __________________________________________________________________________    A 1  0       0   0       0       0                                              2 146      0   0       0       0                                              3 231      0   0       0       0                                            B 1  0       0   0       0       0                                              2 84      20   0       0       0                                              3 53      41   0       0       0                                            C 1  0       0   0       0       0                                              2 42      37   6       0       0                                              3 63      21   12      0       0                                              4 51      24   20      0       0                                              5 36      35   29      0       0                                            D 1  0       0   0       0       0                                              2 31      19   5       3       0                                              3 27      22   14      11      0                                            E 1 19      24   16      6       4                                              2 11      18   15      14      13                                           __________________________________________________________________________

The seizure resistance of sample Nos. C-2 and B-3 as a function of shaftroughness is shown in FIG. 5. The seizure resistance data was determinedin accordance with the conditions listed in Table 2 for seizure tester Aand by varying the shaft roughness as shown in FIG. 5. For comparison,the seizure resistance of a conventional Al-Sn(20)-Cu(1) alloy is alsoshown in FIG. 5. It is seen that seizure resistance of the aluminum basebearing alloy of the invention is improved as the size of the nodular Siparticles is increased and that the seizure resistance of the alloy ofthe invention containing nodular Si particles of a specified number andsize is superior to that of a conventional aluminum base bearing alloy.

The seizure resistance of a thrust bearing of an aluminum base bearingalloy corresponding to sample Nos. C-1 to C-5 of Table B as a functionof the number of nodular Si particles having a size of from 10 to 20 μm(the number of particles being based on a cross section of the alloy of3.56×10⁻² (mm)²) is shown in FIG. 6. The seizure resistance data wasdetermined according to the conditions for seizure tester D listed inTable 2. It is again seen that the seizure resistance of the alloysincreases as the number of large particles increases.

The seizure resistance of alloy sample C-2 of Table B as a function ofoil temperature is shown in FIG. 7. The seizure resistance data wasobtained according to the conditions of seizure tester A listed in Table2 with the oil temperature varied as shown in FIG. 7. It is seen thatthe seizure resistance decreases as the temperature of the lubricatingoil increases but that the seizure resistance is maintained at arelatively high level even at a high oil temperature.

FIG. 8 compares the seizure resistance of alloy sample No. C-2 of TableB with that of a conventional Al-Sn(20)-Cu(1) alloy for a forging shaftand for a nodular graphite cast iron shaft. The data of FIG. 8 wasobtained employing the conditions of seizure tester A of Table 2employing the different shafts. FIG. 8 illustrates that an aluminum basebearing alloy of the present invention provides markedly superiorseizure resistance with the use of a nodular graphite cast iron shaft ascompared to the conventional alloy.

To demonstrate the outstanding seizure and fatigue resistance of thealuminum base bearing alloys according to the present invention havingdifferent Si contents, bearing alloys having an Sn content of 15 wt.%.Pb content of 3 wt.%, Cu content of 0.5 wt.%, Cr content of 0.4 wt.% andSi content as shown in Table C, the balance being Al, were preparedaccording to the process described above and employing the condition ofthe process employed in the present invention listed in Table 1. Theannealing conditions (Step (8), Table 1) were varied so produce nodularSi particles having the number and size distribution listed in Table C.

The data of Table C demonstrates that for each of the Si contents, theseizure resistance of the alloy is increased as the number and size ofthe Si particles increase whereas the fatigue resistance is decreasedslightly for bearing alloys containing larger Si particles.

                                      TABLE C                                     __________________________________________________________________________                                       Seizure Unit Load                                                                      Fatigue Unit Load                 Sample                                                                            Si   Silicon particles per 3.56 × 10.sup.-2 (mm).sup.2                                                 (Seizure tester A)                                                                     (Fatigue tester B)                No. (wt. %)                                                                            <5 μm                                                                           5-10 μm                                                                         10 < -20 μm                                                                        20 < -40 μm                                                                        (kg/cm.sup.2)                                                                          (kg/cm.sup.2)                     __________________________________________________________________________    A-1 0.5  balance                                                                            0    --      --      400      700                               A-2 "    "    3    --      --      450      700                               A-3 "    "    5    --      --      650      700                               A-4 "    "    10   --      --      750      700                               A-5 "    "    30   --      --      800      700                               A-6 "    "    11   5       --      900      700                               A-7 "    "    30   11      2       1,200    650                               A-8 "    "    10   5       1       1,100    700                               A-9 "    "    3    2       --      750      700                               B-1 1.0  "    0    --      --      400      700                               B-2 "    "    5    --      --      650      700                               B-3 "    "    11   --      --      700      700                               B-4 "    "    31   --      --      800      700                               B-5 "    "    11   5       --      900      700                               B-6 "    "    30   11      5       1,300    650                               B-7 "    "    30   5       --      900      700                               B-8 "    "    3    2       --      750      700                               C-1 3.0  "    0    --      --      400      700                               C-2 "    "    5    --      --      650      700                               C-3 "    "    10   --      --      700      700                               C-4 "    "    41   --      --      850      700                               C-5 "    "    41   10      --      1,000    650                               C-6 "    "    65   41      10      1,400    600                               C-7 "    "    3    2       --      800      700                               C-8 "    "    65   --      --      850      700                               C-9 "    "    65   5       --      900      700                               D-1 5.0  balance                                                                            0    --      --      450      700                               D-2 "    "    5    --      --      700      700                               D-3 "    "    21   --      --      800      700                               D-4 "    "    63   21      --      1,000    600                               D-5 "    "    125  63      21      1,400    550                               D-6 "    "    31   5       --      950      700                               D-7 "    "    22   11      5       1,300    600                               D-8 "    "    3    2       --      800      700                               D-9 "    "    125  5       --      950      650                               __________________________________________________________________________

                                      TABLE D                                     __________________________________________________________________________    Si Particles/3.56 × 10.sup.-2 (mm).sup.2                                Sample                                                                            Wt.                                                                              Si particle size (μm)                                                                         Sn                       Seizure                                                                             Fatigue (B)          No. %  <5 5-10                                                                              10 < -20                                                                            20 < -40                                                                            (wt. %)                                                                            Additional Elements (Wt.                                                                          kg/cm.sup.2                                                                         kg/cm.sup.2          __________________________________________________________________________     1  0.5                                                                              bal                                                                              5   --    --    25   Pb(1)                                                                              Cu(2)          650   650                   2  "  "  10   5    --    10   Pb(B)               800   700                   3  "  "  30  11    2     1.5                      1,200 700                   4  "  "  91  --    --    20   Pb(3)                                                                              Cu(0.5)                                                                            Cr(0.5)   900   650                   5  "  "  53  --    --    35   Cr(1)               900   550                   6  "  "  28   3    --    10   Cu(0.3)             1,000 700                   7  "  "  3    2    --    15   Cd(5)               800   700                   8  "  "  8    3    1     15   Pb(3)                                                                              Cr(0.5)        850   700                   9  "  "  24  18    3     5    Cd(2)                                                                              Mg(2)          1,250 650                  10  "  "  10  --    --    30   Cu(1)                                                                              Mg(1)                                                                              Mn(1)     800   550                  11  1.0                                                                              "  5   --    --    5                        600   700                  12  "  "  11   5    --    25   Tl(1)                                                                              Cu(0.5)        800   650                  13  "  "  30  11    5     3    Cr(0.5)             1,200 650                  14  "  "  24  --    --    5    Cu(0.3)                                                                            Cr(0.3)        750   700                  15  "  "  5    3    --    10   Cd(4)                                                                              Cu(0.5)        900   700                  16  "  "  4    1    --    20   Bi(2)                                                                              Mg(0.5)        900   700                  17  "  "  74  --    --    15   Mg(1)               900   700                  18  "  "  78  15    --    10   Cr(0.5)             1,000 700                  19  "  "  42  11    3     5    Pb(3)               1,300 650                  20  "  "  81  --    --    20                       900   650                  21  3.0                                                                              "  10  --    --    5    Pb(2)                                                                              In(2)                                                                              Cu(0.8)                                                                            Cr(0.7)                                                                            700   700                  22  "  "  41  10    --    10   In(2)               1,000 700                  23  "  "  65  41    10    15   Mg(0.5)                                                                            Cr(0.1)        1,400 650                  24  "  "  5   --    --    1.5  Cu(0.8)             550   700                  25  "  "  4    2    --    20   Pb(3)                                                                              Cu(0.1)        650   700                  26  "  "  25   5    --    25   Cd(4)                                                                              Cr(1)          1,000 650                  27  "  "  113 --    --    30   Pb(0.5)                                                                            Cu(2)                                                                              Cr(1)     950   650                  28  "  "  83  21    --    15   Pb(3)                                                                              Tl(0.5)                                                                            Cu(0.3)                                                                            Mn(0.1)                                                                            1,000 700                  29  "  "  42  10    3     10   Pb(3)                                                                              Cu(0.5)                                                                            Cr(0.4)   1,400 650                  30  "  "  37  --    --    30                       950   600                  31  5.0                                                                              "  21  --    --    5    Bi(6)               750   700                  32  "  "  63  21    --    10   Pb(0.5)             1,000 700                  33  "  "  125 63    21    10   In(5)                                                                              Cu(0.5)                                                                            Mg(0.5)   1,400 600                  34  "  "  5   --    --    10   Mg(1)               650   700                  35  "  "  3    2    --    15   Pb(4)                                                                              Cu(0.5)        700   700                  36  "  "  156 --    --    15   Tl(2)               950   600                  37  "  "  85  21    5     10   Cu(0.4)                                                                            Cr(0.3)        1,350 650                  38  "  "  38   5    --    20   Cd(0.5)                                                                            In(0.5)                                                                            Mg(0.1)                                                                            Cr(0.3)                                                                            956   700                  39  "  "  62  --    --    5    Cu(1)               900   700                  40  "  "  37   3    --    10                       950   700                  __________________________________________________________________________

Bearing alloys of the present invention having the compositions andnodular Si particle distribution shown in Table D were preparedemploying the process conditions listed in Table 1. The data of Table Dshow that aluminum base bearing alloys of the present inventioncontaining, in addition to the Si and Sn, Pb, Cd, In, Tl, Bi, Cu, Mg, Crand Mn, alone and in various combinations, also possess outstandingseizure resistance and fatigue resistance properties.

Although the present invention has been described in conjunction withcertain preferred embodiments thereof, it is to be understood that theinvention is not intended to be limited to these embodiments but,instead, is to include all those embodiments within the scope and spiritof the appended claims.

What is claimed is:
 1. An aluminum base bearing alloy consistingessentially of 0.5-5 wt.% Si, 1.5-35 wt.% Sn and, as the balance,aluminum, the alloy containing at least 5 particles of Si per 3.56×10⁻²(mm)² of cross-sectional area thereof, said particles being nodular andhaving a particle size of at least 5 μm.
 2. The aluminum base bearingalloy of claim 1, further comprising 0.5 to 8 wt.% of at least oneelement selected from the group consisting of Pb, In, Tl, Cd and Bi. 3.The aluminum base bearing alloy of claim 1, further comprising 0.5-8wt.% of at least one element selected from the group consisting of Pb,In, Tl, Cd and Bi, and 0.1-2 wt.% of at least one element selected fromthe group consisting of Cu and Mg.
 4. The aluminum base bearing alloy ofclaim 1, further comprising 0.5-8 wt.% of at least one element selectedfrom the group consisting of Pb, In, Tl, Cd and Bi, 0.1-2 wt.% of atleast one element selected from the group consisting of Cu and Mg and0.1-1 wt.% of at least one element selected from the group consisting ofCr and Mn.
 5. The aluminum base bearing alloy of claim 1, furthercomprising 0.1-2 wt.% of at least one element selected from the groupconsisting of Cu and Mg.
 6. The aluminum base bearing alloy of claim 1,further comprising 0.1-2 wt.% of at least one element selected from thegroup consisting of Cu and Mg and 0.1-1 wt.% of at least one elementselected from the group consisting of Cr and Mn.
 7. The aluminum basebearing alloy of claim 1, further comprising 0.1-1 wt.% of at least oneelement selected from the group consisting of Cr and Mn.
 8. The aluminumbase bearing alloy of claim 1, further comprising 0.5-8 wt.% of at leastone element selected from the group consisting of Pb, In, Tl, Cd and Bi,and 0.1-1 wt.% of at least one element selected from the groupconsisting of Cr and Mn.
 9. The aluminum base bearing alloy of claim 4,wherein the total amount of elements other than Al and Si, is less than35 wt.%.
 10. A bearing material which is made by applying the aluminumbase bearing alloy of any of claims 1-9 to a backing steel sheet bypressure welding.